Source Naturals Mastic Gum Extract is standardized to 35% masticonic acids, which are the active compounds shown to support the lining of the stomach and duodenum, and the body's own response to imbalances. Mastic gum is a natural resin from the Pistacia lentiscus tree of Greece and has been used traditionally by Mediterranean cultures to support gastrointestinal health. Each serving delivers 1,000 mg of mastic gum extract along with 38 mg of calcium.